Objective To evaluate the effect of individualized nursing on the failure rates of bracket in adolescents treated by fixed appliances.Methods 120 adolescents treated by fixed appliances were randomly assigned to 4 groups (A,B,C and D).30 females in group A and 30 males in group B were treated by individualized nursing (that is,nurses using language,illustration and texts to help patients in recognition,mentality,behavior) ; 30 females in group C and 30 males in group D were treated by routine nursing.The failure rates of bracket of the four groups were calculated after one month.And it was compared between group A and B,group C and D,group A and C,and group B and D.Results After one month,the failure rates of bracket were 0.20％,0.40％,1.57％ and 1.76％,respectively.Significant differences were not found between group A and B and group C and D (P＞0.05),but were found between group A and C and group B and D (P＜0.05).Conclusions During the orthodontic treatment of adolescents,gender has little effect on the failure rates of bracket.Individualized nursing could improve compliance,thus reduce the failure rates of bracket.

The selective cationic polymerization of isobutylene (IB) initiated by a BF3·cyclohexanol (CL) complex was carried out from the mixed C4 fraction feed containing the 4C saturated and unsaturated hydrocarbons at −20°C. The effects of CL concentration, BF3 concentration, solvent for preparing BF3·CL complex and polymerization time on the chemical structure of end groups, number-average molecular weight (M n) and molecular weight distribution (MWD, M w/M n) of the resulting polymers were investigated. The experimental results indicate that the BF3·CL complex initiating system exhibited an extremely high selectivity toward the cationic polymerization of IB in the mixed C4 fraction feed and low molecular weight (M n = 900–3600) polyisobutylenes (PIBs) with large proportion of exo-double bond end groups were obtained. The exo-double bond content in PIB chain ends increased by increasing CL concentration or by decreasing solvent polarity in initiating system, BF3 concentration and polymerization time. The M n and MWD of the resulting PIBs were dependent on the concentrations of CL and BF3. Highly reactive PIBs with around 90 mol% of exo-double bonds were successfully synthesized by the selective polymerization of IB from the mixed C4 fraction feed, providing a potentially practical process for its simplicity and low costs.

FTIR spectroscopy in combination with a diamond tipped attenuated total reflectance (ATR) immersion probe was utilized to study in situ coordination polymerization of butadiene (Bd) in hexane (HEX) with Neodymium-based catalyst. The relationship of their intensity at signal bands of Bd and its concentration were investigated. The kinetic studies of polymerization of Bd were conducted by in situ ATR-FTIR. The signal band at 1592 cm(-1) was assigned to the stretching vibration of Bd, and the signal bands at 1010 cm(-1) and 904 cm were assigned to the deformation vibration of Bd. The Bd/HEX solution exhibited only the above three signal bands of Bd in the FTIR spectrum, and solvent/interference was negligible when HEX spectrum was chosen as the background. All the intensity Lit the signal bands of 1592, 1010 and 904 cm(-1) were found to be proportional to the Bd concentration in the range of 0.46-3.88 mol(-1), The stronger signal band at 904 cm(-1) was chosen to monitor the Bd concentration during polymerization, and the Bd conversion was calculated on the basis of the linearity dependence of Bd concentration on the corresponding peak intensity at 904 cm(-1). The agreement between the FTIR and conventional (gravimetric) kinetic data is excellent in all four sets of experiments. It is evident that signal hand at 904 cm(-1) can be used for the convenient real-time monitoring of Bd polymerization. The first-order plots were linear at different polymerizations and thus polymerization rate was first order with respect to monomer concentration. The polymerization rate increased with increasing polymerization temperature, and the apparent propagation activation energy was determined to be 56.5 kJ.moL(-1). The GPC traces of polybutadiene products obtained at different polymerization temperatures exhibited relatively narrow unimodal molecular weight distribution, and polydispersity index (M(w)/M(n)) was around 2.5. The molecular weight of resultant polymers increased linearly with monomer conversion. The polybutadienes with high cis-1, 4 configuration ranging from 98.0% to 99.2% and low vinyl configuration of around 0.4% could be prepared with Neodymium-based catalyst, leading to low T(g) and some crystal line formation observed in DSC and POM analysis.

FTIR spectroscopy in combination with a diamond tipped attenuated total reflectance (ATR) immersion probe was utilized to study in situ the copolymerization of butadiene (Bd) and isoprene (Ip) with neodymium-based catalyst in hexane. The relationship between the signal intensity of monomer and its concentration was investigated. The kinetic study of copolymerization of Bd and Ip was further conducted, and the monomer reactivity ratios were determined via in situ ATR FTIR. The signal band at 1010 cm −1 was assigned to wagging vibration of Bd and its intensity was proportional to Bd concentration ([Bd]) in the range of 0.46–3.88 mol·L −1 . The signal bands at 890 and 989 cm −1 were assigned to wagging vibration of Ip and the signal intensity was also proportional to Ip concentration ([Ip]) in the range of 0.08–4.73 mol·L −1 at 890 cm −1 and 0.08−7.49 mol·L −1 at 989 cm −1 , respectively. Thus the signal band at 1010 cm −1 was chosen to monitor Bd concentration and bands at 989 and 890 cm −1 to monitor Ip concentration during the copolymerization, respectively. It was demonstrated that the conversions of Bd and Ip calculated from FTIR data agreed very well with those obtained gravimetrically. The polymerization rates were first order with respect to both [Bd] and [Ip], respectively at different polymerization temperatures. The apparent propagation activation energy for Bd and Ip could be determined to be 54.4 kJ·mol −1 and 57.7 kJ·mol −1 , respectively. The monomer reactivity ratios were calculated to be 1.08 for Bd ( r Bd ) and 0.48 for IP ( r Ip ) based on FTIR data. The Bd-Ip copolymer products with random sequence could be obtained with only one glass transition temperature.

The coordination polymerization of 1,3-butadiene was conducted with Ni(naph)2 /A1R3 /BF3.OEt2 catalyst system in the presence of N,N-dimethyl ethanolamine(DMEA) and octanol(OctOH) in hexane at 50℃.The effects of molar ratios of DMEA /Ni,B /Ni and Al /Ni on monomer conversion,intrinsic viscosity([η]),molecular weight,molecular weight distribution and microstructure of polybutadiene(PB) were investigated.The kinetic study was also conducted for this polymerization at different temperatures ranging from 20℃ to 50℃.The results showed that DMEA and OctOH played very important roles in modifying molecular weight,molecular weight distribution and microstructure.By comparison,the molecular weight of polybutadiene products could be greatly increased,molecular weight distribution narrowed and cis-1,4 content of Bd units in polymer chain increased to 97.8% and 1,2-content decreased to 1.3% by introducing adequate amounts of DMEA and OctOH,leading to more crystalline and less gel content.Furthermore,the intrinsic viscosity([η]) of polymer products could also be modulated by changing the molar ratios of B/Ni and Al /Ni in the range of 2.0 ～ 4.0 dL /g.The polymerization was in first order with respect to monomer concentration at different polymerization temperatures.The apparent activation energy for propagation was determined to be 43.7 kJ.mol-1.

A series of butadiene-isoprene copolymers (BIR) with various compositions were synthesized with a neodymium-based catalyst system. The microstructure, composition and sequence of copolymers were characterized by FTIR and 13C-NMR spectroscopy. The crystallization behavior of the BIR copolymers was investigated by DSC analysis. The results demonstrate that the content of cis-1,4 configuration in both butadiene (Bd) and isoprene (Ip) units are around 98% when Bd content in feed (ƒ Bd) covering the range from 55.7 mol% to 96.0 mol%. The reactivity ratios of Bd and Ip were determined to be 1.40 and 0.48 respectively. The random copolymers of Bd and Ip show only one glass transition temperature (T g) from −107.4°C to −80.5°C, which is dependent on the composition and fits nicely with Fox equation. The sequence distribution followed the first-order Markov statistical model. It is found that the copolymer chains with higher Bd content contain longer polybutadiene (PBd) segments, and the sequence length of PBd segments (N Bd) exhibits great influence on the crystallization behavior of the copolymer. The copolymers with N Bd ≥ 11.8 could crystallize at low temperatures (−71°C to −43°C). The crystallization temperature and enthalpy values decreased gradually with decreasing N Bd. The copolymers with N Bd ≤ 7.9 are amorphous even at very low temperatures (0°C to −150°C) due to the short PBd segments.

The coordination polymerization of 1,3-butadiene was conducted with Ni(naph)(2)/A1R(3)/BF3 center dot OEt2 catalyst system in the presence of N, N-dimethyl ethanolamine (DMEA) and octanol (OctOH) in hexane at 50 degrees C. The effects of molar ratios of DMEA/Ni, B/Ni and Al/Ni on monomer conversion, intrinsic viscosity ([eta]), molecular weight, molecular weight distribution and microstructure of polybutadiene (PB) were investigated. The kinetic study was also conducted for this polymerization at different temperatures ranging from 20 degrees C to 50 degrees C. The results showed that DMEA and OctOH played very important roles in modifying molecular weight, molecular weight distribution and microstructure. By comparison, the molecular weight of polybutadiene products could be greatly increased, molecular weight distribution narrowed and cis-1,4 content of Bd units in polymer chain increased to 97.8% and 1,2-content decreased to 1.3% by introducing adequate amounts of DMEA and OctOH,leading to more crystalline and less gel content. Furthermore, the intrinsic viscosity ([eta]) of polymer products could also be modulated by changing the molar ratios of B/Ni and Al/Ni in the range of 2.0 similar to 4.0 dL/g. The polymerization was in first order with respect to monomer concentration at different polymerization temperatures. The apparent activation energy for propagation was determined to be 43.7 kJ. mol(-1.)

The copolymerization of 4-vinylbenzyl chloride (VBC) and vinyl acetate (VAC) was carried out in toluene at 75°C via radical polymerization using 2,2′-azo-bis-(isobutyronitrile) (AIBN) as an initiator. The random copolymers of poly(4-vinylbenzyl chloride-co-vinyl acetate) (P(VBC-co-VAC)) with number average molecular weight (M n) from 2000 to 6900, relatively narrow molecular weight distribution (MWD, M w/M n ca. 2.0) and with different copolymer composition of 4-vinylbenzyl chloride (VBC) from 17 mol% to 62 mol% could be obtained. The P(VBC-co-VAC) copolymers with an average number of 7 to 13 initiating sites of benzyl chloride per macromolecule could be used for the cationic polymerization of isobutylene (IB). The cationic polymerizations of IB were further conducted by using P(VBC-co-VAC) copolymers as macroinitiators in conjunction with TiCl4 at −40°C in CH2Cl2. The effects of VBC/TiCl4 (molar ratio) on monomer conversion, M n and MWD of the resultant copolymers were investigated under 3 sets of conditions. It is found that P(VBC-co-VAC)-g-PIB copolymers with relatively narrow MWD (M w/M n ca. 2.0) and with terminal tert-chlorine functional groups in branched PIB chains could be successfully synthesized when VBC/TiCl4 (molar ratio) was set in the range from 0.10 to 1.12. The unimodal GPC curve of the P(VBC-co-VAC)-g-PIB copolymers by RI detector was almost in harmony with the GPC curve by UV detector. The TEM image of the P(VBC-co-VAC)-g-PIB copolymer stained by RuO indicated that the copolymer formed a two-phase morphology with P(VBC-co-VAC)-rich domains of 20–100 nm in size tethered by PIB branch segments.

The cationic polymerizations of isobutylene (IB) coinitiated by AlCl 3 were carried out in solvent mixture of n -hexane/methylene dichloride ( n -hex/CH 2 Cl 2 ) of 60/40 V / V in the presence of ethyl benzoate (EB) at various temperatures range from −80°C to −30°C. The effects of EB concentration ([EB]) and polymerization temperature on monomer conversion, weight-average molecular weight ( M w ) and molecular weight distribution (MWD, M w / M n ) of polyisobutylene (PIB) products were investigated. The rate of polymerization decreased while M w of PIB products increased with increasing [EB]. The polymers with high molecular weight could be prepared in the presence of a suitable amount of EB. Significantly, the polymers with high M w of 80.2 × 10 4 and 65.4 × 10 4 could be produced at −80°C and −70°C at [EB] = 0.24 × 10 −3 mol/L respectively, which were much higher than that ( M w = 57.9 × 10 4 ) of PIB prepared at −100°C in the absence of EB. A simple but effective method for preparing the high molecular weight polyisobutylenes was developed in this work. It has been also found that the activation energy for propagation ( E p ) depended on the polymerization temperature range in the presence of EB. An obvious inflection of the linear plots of ln X n versus 1/ T p occurred at the temperature range from −60°C to −50°C at four different concentrations of EB from 0.19 × 10 −3 mol/L to 0.33 × 10 −3 mol/L, and thus the inflection temperature ( T inf ) was in the range of −60°C to −50°C. When [EB] was in the range of 0.24 × 10 −3 mol/L to 0.33 × 10 −3 mol/L, E p was determined to be around −12 kJ/mol when the polymerization was carried out at temperatures from −80°C to T inf and to be around −28 kJ/mol at temperatures from T inf to −15°C respectively.

The carbocationic polymerization of isobutylene(IB)with H_2O/TiCl_4 as initiating system in the presence of pyridine(Py),triethylamine(TEA)or N,N-dimethylacetamide(DMA)was conducted in a mixture of methylene dichloride(CH_2Cl_2)and n-hexane(Hex).The effects of solvent polarity,polymerization temperature and monomer concentration on the conversion,molecular weight(MW)and molecular weight distribution(MWD,M_w/M_n)of polyisobutylene(PIB)were investigated.The polymerization rate increased greatly with an increase in solvent polarity.The polymerization rate and the molecular weight of PIB obtained increased obviously with decreasing the polymerization temperature.The corresponding active energy of propagation(ΔE)was calculated to be-28.8 kJ/mol,-25.8 kJ/mol and-29.0 kJ/mol in the presence of Py,DMA and TEA respectively.The chain transfer side-reaction decreased and molecular weight distribution of PIB products became narrow with decreasing polymerization temperature.The polymer with tert-chlorine end group were obtained at-60℃.Both the monomer conversion and molecular weight of PIB increased with isobutylene concentration([IB]_0≤2.5 mol/L)while molecular weight distribution kept relatively narrow and the polydispersity(M_w/M_n)is around 1.4 and 1.5 for the carbocationic polymerization of IB in the presence of Py and TEA respectively.The constant of chain transfer reaction to monomer(C_M)was calculated to be 5.5×10-4 and 6.6×10-4 for the carbocationic polymerization of IB in the presence of Py and TEA respectively.A desirable polymerization of IB with apparent absence of chain transfer reactions could be obtained by H_2O/TiCl_4 initiating system in the presence of Py or DMA at-60℃ under the appropriate reaction conditions.

The highly reactive polyisobutylenes (PIBs) with alpha-double bonds (87.5 mol%) or tert-chloro (tert-Cl) groups ( 95 mol%) could be prepared via the cationic polymerization of isobutylene (IB) coinitiated by BF3 or TiCl4 respectively. The Friedel-Crafts alkylation of diphenylamine (DPA) with the highly reactive PIB with a alpha-double bonds was further conducted under different conditions, such as at different alkylation temperature, in the mixed solvents of CH2Cl2/n-hexane with different solvent polarity and at DPA concentration ([DPA]). The resultant PIBs with sec-arylamino terminal groups were characterized by GPC with RI/UV dual detectors and H-1-NMR spectrum. The experimental results indicated that alkylation efficiency increased with increases in reaction temperature, solvent polarity and [DPA]. The 77 mol% of sec-arylamino terminated PIBs could be obtained in 10/90 (V/V) mixture of nHex/CH2Cl2 with [DPA]/[PIB]of 3.0 at 60 degrees C for 45 h. Moreover, the alkylation of DPA with highly reactive PIBs with mainly tert-Cl terminal groups was also carried out in 10/90 (V/V) mixture of CH2Cl2/nHex with [DPA]/[PIB]=3.0 at 60 degrees C for 45 h, and almost monoalkylation with 100 mol% sec-arylamino terminal groups could be achieved. These results will help further explorations of the molecular engineering via combination of cationic polymerization with alkylation.

The polycondensation of L-aspartic acid (A) was conducted in a mixed solvent of sulpholane and 1,3,5-trimethylbenzene with phosphoric acid (φ=85%) as catalyst, using microwave irradiation. The effects of varying the dosage of phosphoric acid catalyst, microwave power, reaction temperature and time on the yield, average molecular weight and molecular weight distribution (MWD, Mw/Mn) of the resulting polymer products, poly(succinimide) (PSI) and poly(aspartic acid), was investigated. The product polymers, were characterized by FT-IR. The results indicated that, compared with the traditional method, under microwave irradiation the polymerization time could be significantly reduced from 3-5 h to 20 min, and the reaction temperature (170-200 ℃) required was also reduced. The yield and molecular weight increased with increasing reaction temperature and time. All the GPC traces of the poly(aspartic acid) products obtained with different concentrations of catalyst exhibited narrow and unimodal molecular weight distributions with number-average molecular weight (Mn) from 6000 to 20000 and polydispersity from 1.3 to 2.4.

The polymerization of styrene(St) with a modified rare earth catalyst system composed of neodymium tricarboxylate(Nd),triisobutyl aluminium(Al) and n-butyl chloride(BCL) was carried out in cyclohexane.The effects of preparation procedure of the catalyst system(the molar ratios of Al/Nd and of BCL/Nd,ageing temperature and ageing time) and reaction conditions(catalyst concentration,polymerization temperature and polymerization time) on St polymerization,catalytic activity,molecular weight and molecular weight distribution of the resultant polymers were investigated.The catalytic activity depended mainly on the molar ratios of Al/Nd and BCL/Nd,the catalyst concentration,the polymerization temperature and time.High molecular weight of polystyrene could be obtained with the catalyst with low Al/Nd and BCL/Nd ratios aged at relatively low temperature for relatively short time.The molecular weight of polymers increased with a decrease in polymerization temperature.The optimum conditions for obtaining high molecular weight polystyrene are as follows:Al/Nd=8-12(molar ratio),BCL/Nd=5-25(molar ratio),T_a=40-50℃,t_a=6～20?h,Nd/St=1.5×10~(-4)-6.0×10~(-4)(molar ratio),T_p=40～50℃.The molecular weight of the polymers reached high weight-average(M_w) values(M_w=7.6×10~5 g mol~(1)) when Al/Nd=10.The molecular weight decreased and molecular weight distribution became broad when excess Al or BCL existed in the catalyst system.The polymer obtained was extracted by 2-butanone and then separated into an insoluble fraction and a soluble fraction.The DSC characterization of the insoluble fraction shows that its melting point is around 268℃,which indicating that the insoluble fraction mainly contains syndiotactic polystyrene.It is shown from polarized optical micrograph that the soluble fraction also contains some segments with high stereo-regularity.

The mechanism and new stage in controlled/living cationic polymerization of vinyl monomers, such as isobutylene, styrene, vinyl ether, are reviewed. The novel initiating systems including metallocene, Lewis acid with a weak base, Lewis acidic diboranes, water-tolerant acid, and the cationic polymerization in aqueous media are summerized. The advanced thermoplastic elastomer based on polyisobutylene via controlled/living cationic polymerization is used as biomaterials.