The influence of the molecular weight on the crystallization and crystalline phase transformation in polymorphic polybutene-1 (PB-1) is a controversial issue in literature. We suppose the main reason comes from the used commercial samples with broad molecular weight distribution (MWD). To overcome this, one homo-polymer PB-1 resin is effectively separated by solvent gradient fractionation (SGF) according to molecular weight to obtain fractions with narrow MWD for the first time. The appropriate solvent system is selected, i.e. the good solvent and poor solvent are 1,2,4-trimethylbenzene (TMB) and n-butyl cellosolve (BCS), respectively. Most of fractions have narrow polydispersity index less than 1.4. The molecular weights of SGF fractions gradually increase from 3.19 x 10(4) g/mol to 1.21 x 10(6) g/mol when the content of good solvent increases in the mixed solvent. In addition, the influence of the molecular weight on the transformation from Form II to Form I at 25 degrees C is investigated by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) methods. It is found that the higher molecular weight is beneficial to the transformation in the initial stage (0-8h) and the lower molecular weight is beneficial to the transformation in the late stage (over 72h), i.e. the molecular weight has a double influence on the transformation rate from Form II to Form I. And the reasons are also discussed. Our results clarify the influence of molecular weight on transformation from Form II to Form I for PB-1 resin at 25 degrees C.

Elution behavior of chitosan was studied using narrow-bore size exclusion chromatography (SEC) columns packed with 8 mu m porous particles at different eluent flow rates. Delayed elution of the largest chitosan species from the columns was observed at high flow rates, which was attributable to strong chain deformation rather than chain degradation. In particular, a chromatographic mode transition from SEC to slalom chromatography (SC) was observed for high molar mass chitosan samples with abnormal elution behaviors, which originates from the coil - stretch transition of chitosan chains in elongational flow through the columns. By properly reducing the elongational rate in the columns via tuning the flow rate, particle size and column dimension, the chromatographic mode transition from SEC to SC for chitosan can be effectively suppressed.

Generally, commercial P-TREF (preparative temperature rising elution fractionation) equipment carries out an experiment for polyolefin samples between room temperature (or the lowest temperature at 20 degrees C) and 150 degrees C. Although we have applied the traditional TREF method in polyethylene and propylene resin in our previous studies, it failed to fractionate poly(1-butene) with a polymorph structure. Up to now, it has been a challenge to realize an effective P-TREF separation procedure for poly(1-butene) resins. Based on the analysis and experiments, it was found that a low temperature was important for poly(1-butene) resin. Herein, a novel P-TREF instrument with a broad temperature range from -80 to 150 degrees C is designed and fabricated. By applying this equipment, one poly(1-butene) copolymer, i.e., 1-butene/ethylene random copolymer, is first effectively fractionated according to its crystallizability by the TREF principle. The main fractions are eluted at 30, 42, and 46 degrees C, corresponding to the weight percent of 12.81%, 18.05%, and 39.52%, respectively. Chain microstructures of the original resin and its fractions are further characterized by high-temperature gel permeation chromatography coupled with triple detectors (refractive index-laser light scattering-viscometer), C-13-nuclear magnetic resonance spectroscopy (C-13 NMR), and differential scanning calorimetry (DSC). With an increasing elution temperature from -30 to 46 degrees C, the ethylene content of the fractions decreases from 12.6 to 2.9 mol %; meanwhile, the isotacticity increases from 41.2% to 83.6%, and the crystallinity increases gradually. From these results, the TREF technique can be extended to resins (for example, poly(1-butene) copolymer) with slow crystallization kinetics, and the chain microstructure of polymorphic poly(1-butene) copolymer can be analyzed in detail. This will lay a foundation for both basic research and industry applications.

Both fully (98%) and partially (88%) hydrolyzed poly(vinyl alcohol) (PVA) are characterized by aqueous gel permeation chromatography (GPC) coupled with multi-angle laser light scattering. Polymer adsorption on hydrophilic GPC columns is observed for partially hydrolyzed PVA but not for fully hydrolyzed PVA, which is driven by the hydrophobic interactions between the residual acetate groups on PVA and the stationary phase. Desorption of these partially hydrolyzed PVA chains from the packing materials is monitored by decay of the light scattering signal. It is found that the desorption of these polymer chains from porous particles is non-exponential and follows stretched exponential kinetics with index 0.36. It is also shown that asymmetric flow field flow fractionation can be successfully used for the molar mass characterization of PVA, irrespective of the degree of hydrolysis.

One low density polyethylene (LDPE) resin with high-speed extrusion coating property is fractionated through solvent gradient fractionation (SGF) technique using 1,2,4-trimethylbenzene (TMB) and ethyl cellosolve (ECS) as good/poor solvent pair at 115 °C. The pristine sample and its fractions are characterized by high-temperature gel permeation chromatography (HT-GPC) coupled with triple detectors (refractive index RI, light scattering LS, viscometer VIS), 13C–nuclear magnetic resonance spectroscopy (13C–NMR), differential scanning calorimetry (DSC) and successive self-nucleation/annealing (SSA) thermal fractionation. By adjusting the ratio of good/poor solvent, the obtained fractions show their molecular weight from 1.58 × 103 g/mol to 4.76 × 105 g/mol. It is found that the fractions with high molecular weight (fractions 10–13) occupy about 55.85% in resin. Particularly, the molecular weight distribution (MWD) of most fractions is in the range of 1.1–1.2. Each fraction contains more short chain branch (SCB) and less long chain branch (LCB) simultaneously. With increasing the molecular weight, the branching content shows no regular change. The lowest SCB and total branch content regions correspond to molecular weight 1.97 × 104 to 4.10 × 104 g/mol. The melting and crystallization temperatures of fractions firstly increase and then decrease with the molecular weight. The crystallinity decreases gradually from 51.7% to 31.1%. In the SSA thermal fractionation, each fraction shows a broad range of endotherm with multiple melting peaks in DSC curve corresponding to the different methylene sequence length (MSL) (L n and L w ). The longest L n (L w ) region occurs in the molecular weight of 8.95 × 103 to 3.14 × 104 g/mol. The relationship between chain microstructure and properties is also discussed.

Here we present SEC-MALLS study for chitosan samples with weight average molar mass Mw between 33 and 427 kg/mol on columns packed with 8 μm porous particles. A low injection concentration on the order of 0.1-0.2 mg/mL must be used to avoid overloading of the SEC columns, due to the extended coil conformation of cationic chitosan in the dilute acid buffer as compared to neutral polymers. Additionally, SEC must be performed at an eluent flow rate no more than 0.5 mL/min for high molar mass chitosan samples. At flow rates of 1.0 and 1.5 mL/min, the elution of the largest chitosan species is delayed, which leads to a distortion of the molar mass distribution towards lower molar mass region. Such an abnormal behavior is due to a chromatographic mode transition from SEC to slalom chromatography, originated from the coil-stretch transition of chitosan chains in elongational flow through the packed columns.

Quantitative size exclusion chromatography (SEC) was exploited to study the composition, molecular weight and molecular weight distribution of aqueous two-phase system of dextran and poly(ethylene glycol) (PEG) following phase separation. Tie lines constructed by SEC method were compared with the cloud point curve of the system obtained by titration. An excellent agreement was found between the tie line end points and the cloud point, except for the data points of the PEG-rich phases close to the critical point. The molecular weight and molecular weight distribution of the two polymer species in two co-existing phases obtained by SEC indicate that the mismatch is caused by the uneven distribution of macromolecular components between two phases upon phase separation. Having a broad molecular weight distribution, dextran in the two phases show prominent molecular mass difference. The molecular weight of dextran in the dextran-rich phase is significantly higher than that in the PEG-rich phase. As the initial polymer concentration of the system increases, the molecular weight difference of dextran in the two phases becomes more significant. However, we have not observed such a trend for PEG because of its narrow molecular weight distribution. Accurate data on the phase diagram and molecular weight of two polymer components in the co-existing phases can be obtained using quantitative SEC. The above results will not only help to understand the phase diagram of dextran-PEG-water ternary system, but also provide guidance to its application in extraction and separation of biological materials.

A complex branched polyethylene resin with excellent processing and film-forming properties is fractionated through solvent gradient fractionation (SGF) technique. Here, the good solvent is 1,2,4-trimethylbenzene (TMB) and poor solvent is ethyl cellosolve (ECS). The fractions are further analyzed using high-temperature gel permeation chromatography (GPC) coupled with triple detectors (refractive index (RI)-light scattering (LS)-viscometer (VIS)), and 13C-nuclear magnetic resonance spectroscopy (13C-NMR). The molecular weight distribution of SGF fractions is very narrow, most of them are less than 1.1. The molecular weights of SGF fractions gradually increase as the content of good solvent increases in the mixture. The fractions with different molecular weights all have branching structure, the short chain branching is major in all fractions and along with certain content of long chain branching. Branching distribution across the molecular weight distribution is discussed in detail, and branching distribution within a SGF fraction is also researched.

The band broadening of aqueous gel permeation chromatography columns was studied by coupling with a multi. angle laser light scattering detector, using narrow polyethylene glycol( PEG) and polyethylene oxide( PEO) samples. The determined spreading factor of PEG/PEO increased with increasing molecular weight between 4. 0 x 10(3) and 1.3 x 10(6). True molecular weight distributions of these samples were obtained with band broadening correction. Despite the presence of band broadening in the columns, the monodisperse scaling law between radius of gyration and molecular weight of PEO is established to be R-gz = 0. 0272 M-w (0. 56), indicating that the long PEO chains take a swollen random coil conformation in water due to the presence of excluded volume effect.

A series of copolymers of ethylene with 1-hexene synthesized using a metallocene catalyst are selected and mixed. The blend is fractionated via preparative temperature rising elution fractionation (P-TREF). All fractions are characterized via high-temperature gel permeation chromatography (GPC), 13C nuclear magnetic resonance spectroscopy (13C-NMR), and differential scanning calorimetry (DSC). The changes in the DSC melting peak temperatures of the fractions from P-TREF as a function of elution temperature are almost linear, thereby providing a reference through which the elution temperature of TREF experiments could be selected. Moreover, the standard calibration curve (ethylene/1-hexene) of P-TREF is established, which relates to the degree of short-chain branching of the fractions. The standard calibration curve of P-TREF is beneficial to study on the complicated branching structure of polyethylene. A convenient method for selecting the fractionation temperature for TREF experiments is elaborated. The polyethylene sample is fractionated via successive self-nucleation and annealing (SSA) thermal fractionation. A multiple-melting endotherm is obtained through the final DSC heating scan for the sample after SSA thermal fractionation. A series of fractionation temperatures are then selected through the relationship between the DSC melting peak temperature and TREF elution temperature.

The typical standard long chain branching (LCB) polyethylene (PE) SRM1476 is issued by the American National Bureau of Standards, which is widely used as a standard reference material in chromatographic experiments. Although some works have been reported in literatures, they are not consistent, such as the data about its molecular weight and molecular weight distribution. Therefore, it is necessary to further investigate the microstructure features of SRM1476 in order to better serve as a reference object in comparison with other unknown resins. In this study, the molecular chain heterogeneity of SRM1476 is investigated extensively and compared with the linear PE SRM1475. Based on the characterization of the original sample, SRM1476 actually has both LCB and short chain branching (SCB) structures, as well as the SCB content is more than LCB content in 13C-NMR results. After successive self-nucleation and annealing (SSA) thermal fractionation, SRM1476 shows a broad-range endotherm with multiple melting peaks (more than eight peaks), which proves the molecular chain heterogeneity in SRM1476. SRM1476 is fractionated into nine fractions by preparative temperature rising elution fractionation (TREF). At the high elution temperature region, the amounts of fractions are more than 90 %, and their molecular weights are higher. At the low elution temperature region below 50 °C, molecular weights of fractions are lower and their amounts are less than 5 %. Differential scanning calorimetry (DSC) melting curves of TREF fractions with higher elution temperatures shift toward higher temperature with sharper melting peaks. In the results of TREF-SSA cross-fractionation, each fraction shows a broad-range endotherm with multiple melting peaks that shift toward the high elution temperature region with the elution temperature. The arithmetic mean methylene sequence lengths of TREF fractions gradually increase from 33 to 105 as elution temperature increases. Results from TREF-DSC and TREF-SSA cross-fractionations indicate that SRM1476 and its TREF fractions have both intramolecular and intermolecular heterogeneity.

A branched polyethylene resin was selected as an example to study the effects of experimental parameters of successive self-nucleation and annealing method on the results of thermal fractionation. Experimental parameters, such as the first selected self-seeding temperature (T-s), heating and cooling temperature rates, temperature interval (Delta T), and the permanence time at T-s, are studied extensively in successive self-nucleation and annealing (SSA) thermal fractionation. A series of optimized parameters are obtained, which provide the reference for its application. In addition, the results from step crystallization (SC) and SSA thermal fractionations are compared carefully.

Two polyethylene (PE) resins (samples A and B) are synthesized as high-speed extrusion coatings with similar minimum coating thickness and neck-in performance but different maximum coating speeds. Both samples are separated into seven fractions using preparative temperature rising elution fractionation. The microstructures of the original samples and their fractions are studied by high-temperature gel permeation chromatography, Fourier transform infrared spectroscopy, 13C nuclear magnetic resonance spectroscopy, differential scanning calorimetry, and successive self-nucleation/annealing thermal fractionation. Compared with sample B, sample A has a broader MWD, more LCB contents, and less SCB contents. Moreover, sample A contains slightly more 30 °C and 50 °C fractions with lower molecular weights, and more fractions at 75 °C and 85 °C with higher molecular weight. The chain structure and its distribution in the two PE resins are studied in detail, and the relationship between the chain structure and resin properties is also discussed.

A low-density polyethylene (LDPE) resin with excellent processing and film-forming properties is fractionated through temperature rising elution fractionation (TREF) technique. The chain structures of both the original resin and its fractions are further analyzed using high-temperature gel permeation chromatography (GPC) coupled with triple detectors (refractive index (RI)-light scattering (LS)-viscometer (VIS)), 13C-nuclear magnetic resonance spectroscopy (13C-NMR), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and successive self-nucleation/annealing (SSA) thermal fractionation. The 13C-NMR results show that the original resin has both short chain branch (SCB) (2.82 mol%) and long chain branch (LCB) (0.52 mol%) structures. The FTIR results indicate that the methyl numbers (per 1000 C) of the fractions gradually decrease from 81 to 46 with increasing elution temperature from 25 °C to 75 °C. The TREF-GPC cross-fractionation results show that the main component is collected at around 68 °C. The molecular weight of the components in the high elution temperatures of 60 °C to 75 °C is from 2.0 × 103 g/mol to 2.0 × 106 g/mol, and the relative amount is more than 80%. In the low elution temperature region below 50 °C, the molecular weights of the components range from 1.0 × 103 g/mol to 1.6 × 104 g/mol, and the relative amount is less than 10%. In the DSC results, the melting peaks of the fractions gradually increase from 80.1 °C to 108.8 °C with elution temperature. In the SSA thermal fractionation, each resin fraction shows a broad range of endotherm with multiple melting peaks (more than eight peaks). The melting peaks shift toward high temperatures with the elution temperature. The characteristic chain microstructure for the resin is also discussed in detail.

Two low density polyethylene resins (sample A and sample B) were fractionated through temperature rising elution fractionation (TREF), and GPC,C-13-NMR, DSC and SSA are exploited to study the chain structure of original resins and their fractions. The two resins with unimodal distribution have different properties. Compared with sample B, sample A possesses higher tensile break strength and film puncture resistance. By(13) C-NMR, the total branch contents of samples A and B are 3. 93 mol% and 4. 82 mol%, respectively. Both resins have short chain branch and long chain branch structures. It is also found that the branching content of the fractions decreases with the elution temperature, which is in accordance with TREF mechanism. By the TREF-GPC cross-fractionation results, the fractions of two resins focus on higher temperature region. The dominant fraction of sample A is eluted at 80 C, and its molecular weight is concentrated at 32 x 10(4). The dominant fraction of sample B is eluted at 75 CC, and its molecular weight is concentrated at 18 x 104. Sample A has a slightly higher molecular weight, more content on high molecular weight, broader molecular weight distribution. In DSC results, the melting temperatures of samples A and B are 110. 5 degrees C and 110. 2 degrees C, respectively. Both samples have broader melting range corresponding to 50 similar to 120 degrees C. In the SSA thermal fractionation, each fraction of the two samples shows a broad range endotherm with multiple melting peaks (more than eight peaks). The arithmetic mean methylene sequence length of fractions for the two samples gradually increases from 34 to 86 and from 32 to 84 with the increase in the elution temperature, respectively. In addition, the characteristics of chain microstructure and the relationship of structure and properties were discussed.

A series of the copolymers of ethylene with 1-hexene (M1-M9) synthesized by metallocene catalyst Et[Ind]2ZrCl2/MAO was studied by differential scanning calorimetry and successive self-nucleation and annealing (SSA) thermal fractionation. The distribution of methylene sequence length (MSL) in the different copolymers was determined using the SSA method. The comonomer contents of samples M4 and M5 are 2.04 mol% and 2.78 mol%, respectively. Both M4 and M5 have low comonomer content and their MSL distribution profiles exhibit a monotonous increase trend with their MSL. The longest MSL of M5 is 167, and its corresponding molar percent is 43.95%, which is higher than that of M4. Moreover, the melting temperature (T m) of M5 is also higher than that of M4. The comonomer contents of samples M7, M8, and M9 are 8.73 mol%, 14.18 mol% and 15.05 mol%, respectively. M7, M8, and M9 have high comonomer contents, and their MSL distribution profiles display unimodality. M7 has a lower peak value of 33 and a narrow MSL distribution, resulting in a T m lower than that of M8 and M9. The MSL and its distribution are also key points that influence the melting behavior of copolymers. Sometimes, MSL and its distribution of copolymers have a greater impact on it than the total comonomer contents, which is different from traditional views.

Novel thermoresponsive copolymers of zwitterionic sulfobetaine methacrylate (SBMA)‐ and N,N‐dimethylaminoethyl methacrylate (DMAEMA)‐grafted silica nanoparticles are prepared via surface‐initiated atom transfer radical polymerization. The phase behavior of these nanoparticles is investigated. The hybrid nanoparticles exhibit tunable phase transition temperature between the upper critical solution temperature (UCST) and the lower critical solution temperature (LCST) in aqueous solution. A high PSBMA content in P(SBMA‐co‐DMAEMA) copolymer in the hybrid nanoparticles leads to aggregation at low temperatures because of dominant electrostatic interactions of ionic pairs, whereas a relatively low PSBMA content in the hybrid nanoparticles results in a phase transition at high temperatures as a result of predominant hydrophobic interactions of the PDMAEMA. Interestingly, hybrid nanoparticles with a suitable molar ratio of SBMA/DMAEMA exhibit both UCST and LCST in aqueous solution, where the water‐insoluble microdomains of hybrid nanoparticles are generated by the PSBMA or PDMAEMA region depending on the temperature. The above dual‐thermoresponsive phase transition is also controllable in salt solution. A facile change in the molar content of copolymer grafted on silica nanoparticles will tune the UCST and LCST readily. image

The adsorption-desorption of silica nanoparticles(NPs) on poly(ethylene glycol)(PEG) grafted onto gold(Au) substrate was studied by quartz crystal microbalance with dissipation monitoring(QCM-D) technique. The results of frequency and dissipation show that SiO 2 NPs can be adsorbed strongly on PEG-SH brushes at pH of 9.6, and a new dense and rigid construction is formed. Adjusting the pH from 9.6 to 12.3 resulted in the desorption of silica NPs from the PEG brushes because of a significant weakening of the hydrogen bond between the silica NPs and PEG chains. In addition, the viscoelastic properties of the system during the adsorption-desorption process were also analyzed via the relationship between the normalized frequency(Δ f/n ) and mass. And the corresponding atomic force microscopy(AFM) images also exhibit morphological changes during the above process, consistent with the changes in viscoelasticity.

A mixed system that includes poly(ethylene oxide) (PEO) and silica (SiO 2 ) nanoparticles is prepared using two mixing methods. The interaction between PEO and the SiO 2 nanoparticles in the dilute basic solution is investigated using the dynamic light scattering (DLS) and isothermal titration calorimetry (ITC) techniques. The DLS results show qualitatively that SiO 2 nanoparticles interact with both random coils and aggregates of PEO through hydrogen bonding, and PEO-SiO 2 complexes are formed. The degree of disaggregation of aggregates of PEO is readily adjusted by changing the concentration of SiO 2 nanoparticle suspensions. Moreover, the ITC results also certify quantitatively the interaction between PEO and SiO 2 nanoparticle, and give the evidence of formation of PEO-SiO 2 complex.

Temperature dependence of chain conformation and local rigidity of two soluble isomerized polyimides (PIs), poly(hexafluorodianhydride/3,3′-dimethylbenzidine)[poly(6FDA/3,3′-DMB)] and poly(hexafluorodianhy-dride/2,2′-dimethylbenzidine)[poly(6FDA/2,2′-DMB)] were investigated by dilute solution viscosity, size exclusion chromatography(SEC) coupled with multi-angle laser light scattering, viscometer, and refractive index detector in dimethylformamide(DMF) with either 0.1 mol/L LiBr or 3.1 mmol/L tetrabutylammonium bromide(TBAB) in the temperature range of 30 to 50 °C. The scaling relationships of [η]=K η M α and R g=K g M ν obtained are employed to investigate the temperature dependence of chain conformation for the two polyimides. The values of α and ν are in the range of 0.66–0.69 and 0.53–0.56, respectively, for poly(6FDA/3,3′-DMB), meanwhile they are in the range of 0.64–0.68 and 0.53–0.56, respectively, for poly(6FDA/2,2′-DMB). These results reveal that random coil conformations for both PIs are not affected visibly with increasing temperature from 30 °C to 50 °C. However, values of more exact intrinsic viscosity from dilute solution measurement indicate there is only tiny coil extension or shrinkage for both PIs with temperature rising. Parameters related to chain flexibility of polymer, including persistence length l p, shift factor M L (relative molecular weight per unit contour length) and backbone diameter d are estimated from the relationship between intrinsic viscosity and molecular weight for the continuous wormlike cylinder model, which indicates that two samples are flexible chains, only the chain of poly(6FDA/3,3′-DMB) is stiffer than that of poly(6FDA/2,2′-DMB) slightly.