A kinetic study of the living carbocationic polymerization of isobutylene using a 1,4-bis(2-chloro-2-propy1)benzene (dicumyl chloride) (DCC)/TiC14 initiating system in conjunction with pyridine as an externally added Lewis base, in mixed hexanelmethyl chloride cosolvents was conducted utilizing a wide variety of conditions. The investigation revealed that at -80 "C the rate of polymerization was first-order in monomer concentration, first-order in the concentration of the initiator DCC, and secondorder in coinitiator (Tic141 concentration and was proportional to the -0.28 power of the pyridine concentration. In addition, the rate of polymerization was found to decrease with increasing temperature and to increase with increases in solvent polarity. It was also revealed that only ion-paired chain carriers participate in propagation. These results are consistent with a mechanism in which propagation is a simple bimolecular reaction between active polyisobutylene (PIB) chain ends and monomer, and the concentration of active PIB chains is determined by an equilibrium between active and dormant species. IntroductionThe development of living cationic polymerization of isobutylene (IB) may be traced to the early 1980s for polymerizations employing the so-called "quasiliving" polymerization technique, that was reported for a number of cationically polymerizable monomers including a-methylstyrenel and IB.2 This method was carried out under conditions of monomer starvation and, for the case of IB, involved one of several reported initiators, Tic14 as coinitiator, and 60/40 (v/v) hexane/methylene chloride as cosolvents.2 Living characteristics were attributed to rapid initiation, suppression of chain transfer to monomer, and reversibility of termination,
Isobutylene polymerization was initiated using the cumyl chloride/TiCl4/2,4-dimethylpyridine system ([IB] ) 1.0 M, [CumCl] ) 2.3 × 10 -2 M, [TiCl4] ) 0.24 M, [DMP] ) 2.4 × 10 -3 M). Polymerization kinetics in 60/40 hexane/MeCl at -80 °C showed that an IB conversion of ∼98% was reached in 70 s. The active centers were monitored over time at high conversion, by 1 H NMR after quenching with MeOH or allyltrimethylsilane (ATMS), and by GPC after a second addition of IB. Quenching with MeOH or ATMS at times up to 70 s yielded quantitative tert-chloride or allyl chain ends, respectively. For longer periods up to 12 h, MeOH-quenched PIB showed increasing depletion of tert-chloride chain ends of the normal structure (but no appearance of olefin) and ATMS quenching yielded a gradual reduction in allylation to 78% at 12 h. Real-time 1 H NMR of an active polymerization mixture also indicated depletion of tert-chloride end groups. GPC results showed that coupling of PIB chains was not occurring and that a second charge of IB was slowly initiated. The latter process caused a fraction of the chain ends to be restored with normal tert-chloride groups. It was hypothesized that normal tert-chloride chain ends slowly undergo carbenium ion rearrangement to form a mixture of isomerized chain end structures. This process represents the dominant chain interrupting event in TiCl 4-co-initiated IB polymerization under these conditions. The rearranged structures were hypothesized to result from combinations of 1,2-hydride and 1,2-methide shifts; 1 H NMR analysis of a dehydrochlorinated sample was consistent with this interpretation. The rate of depletion of tert-chloride end groups was shown to follow first-order kinetics with an apparent rate constant of 8 × 10 -5 s -1 . The ratio of rate constants for propagation and rearrangement, kp/kr, was calculated to be 3 × 10 4 M -1 .
Design of antimicrobial polymers for enhancing healthcare issues and minimizing environmental problems is an important endeavor with both fundamental and practical implications. Quaternary ammonium silane-functionalized methacrylate (QAMS) represents an example of antimicrobial macromonomers synthesized by a sol-gel chemical route; these compounds possess flexible Si-O-Si bonds. In present work, a partially-hydrolyzed QAMS copolymerized with bis-GMA is introduced. This methacrylate resin was shown to possess desirable mechanical properties with both a high degree of conversion and minimal polymerization shrinkage. Kill-on-contact microbiocidal activities of this resin were demonstrated using single-species biofilms of Streptococcus mutans (ATCC 36558), Actinomyces naeslundii (ATCC 12104) and Candida albicans (ATCC 90028). Improved mechanical properties after hydration provided the proof-of-concept that QAMS-incorporated resin exhibits self-repair potential via water-induced condensation of organic modified silicate (ormosil) phases within the polymerized resin matrix.
The initiation and propagation of isobutylene (IB) polymerization initiated by 1,2-epoxi-2,4,4-trimethylpentane (TMPO-1)/TiCl 4 was monitored by a new fiber-optic transmission mid-IR probe. The real-time IR data provided insight into the initiation mechanism. Polyether formation, isomerization of the TMPO-1 into 2,4,4-trimethylpentanal, and its complexation by TiCl4 were observed, which occurred simultaneously with initiation of IB polymerization. The proposed initiating mechanism involves the formation of tertiary carbocations, which has been claimed to occur in the cationic polymerization of epoxides by the SN1 mechanism. On the basis of our results, the competitive occurrence of both SN1 and SN2 pathways is proposed. Interestingly, ketone/TiCl4 systems were found to initiate IB polymerization, albeit with very low efficiency. IR monitoring of these systems gave additional insight into the initiating mechanism. IB polymerization was monitored by following the disappearance of the second overtone of the C-H wag in the dCH2 group in IB at 1780 cm -1 and the CdC stretch at 1655 cm -1 . The linearity of first-order monomer consumption plots and the production of nearly uniform polyisobutylenes (PIBs) (Mw/Mn ) 1.06-1.13) indicated living conditions.
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