Novel Vinyl Chliride(CO) Polymers Synthesized By Self-stabilization Pricipitation Polymerization And The Application Of The Copolymers

Poly(vinyl chloride)(PVC)is one of the most important general plastics and has wide applications in various fields,such as building,food packaging,toys,biomedical and electronic devices due to its excellent physical and chemical properties and low price.To date,the PVC production capacity in China reach up to about 20 Mt/a.However,the high-value and special PVC resins are still in short supply.Industrially,the PVC resins are mainly produced by suspension and emulsion polymerization which have some limitations,such as the residual of dispersant or emulsifier.Therefore,to develop a novel method for the synthesizing PVC and its copolymers is of importance.In this thesis,the method of self-stabilized precipitation polymerization(2SP)was exploited to the polymerization of vinyl chloride.Firstly,the reactant composition,reaction conditions,the mechanism of polymerization reaction and the PVC particles formation in the 2SP were systematically investigated.On the basis of the successful realization of the 2SP of vinyl chloride,the technology was further extended to the binary copolymerization of vinyl chloride with vinyl acetate or acrylic acid,and the ternary copolymerization of vinyl chloride,vinyl acetate and butyl acrylate.A series of PVC copolymers were synthesized and their applications as PVC additives were investigated.Follows are main results:1.The principle of solvent selection for 2SP of VCM was proposed based on the study of a range of solvents with different polarity.The polymerization of VCM in different solvents is mainly affected by solvent polarity and hydrogen bonding.Taking the ?P and ?H(Hansen Solubility Parameters)as coordinates and the ?P and ?H of PVC as the origin,the solvents those outside the circle with a radius of R=3.4 are suitable for the 2SP of VCM,while the solvents within this range are good solvents for PVC.By investigating the effects of polymerization conditions such as different solvents,monomer and initiator concentration,and reaction temperature on the 2SP of VCM,a mechanism for the polymerization reaction and the PVC particles formation was proposed.In the 2SP of VCM,the mixture of solvent and PVC separates into two phases,a dilute solvent phase and PVC enriched phase.With the increase of monomer conversion,the polymerization of VCM mainly occurred in the PVC enriched phase,where the chain termination rate decreased and the Mn of PVC increased.When the concentration of residual VCM in the system was lower than 10?15 wt%,the Mn of PVC decreased significantly.By tuning the polymerization conditions,PVC resin with Mn range from 4000 to 40000 could be obtained.The mechanism of PVC particle formation can be descriped as followings:PVC molecular chains are insoluble in solvents and precipitate out of the solvents and form micro-domains with very small particle sizes.These micro-domains are thermodynamically unstable because of its high surface energy,thereby aggregate into domains with a diameter of 50?100 nm to reduce the surface energy.As the polymerization continues,these domain structures act as the nuclei of the primary particles by capturing the VCM and allowing it to continue to converge internally.Meanwhile,these domain structures also capture the newly formed PVC chains and aggregating the small domain structures and eventually growing into the primary particles.At low stirring rate,the primary particles aggregate to form larger particles and loose structure.However,these aggregates can be disintegrated into primary particles under strong stirring.In addition,by adding crosslinking agent in the 2SP system of VCM,the Mn of PVC can be significantly increased.For example,PVC with polymerization degree of 1250 could be obtained by introducing 0.25 wt%diallyl phthalate as the crosslinking agent.2.The copolymer of VCM and VAc was carried out by the 2SP and their binary copolymer(PVVA)was prepared successfully.The effect of introduced VAc on the 2SP of VCM was investigated systematically.On the one hand,VAc served as a good solvent of PVC enhance the dissolve or swell ability of the reactant mixture to the copolymer.On the other hand,the introduced PVAc chain segments in PVVA also enhances the solubility of copolymer in solvent.The mass fraction of PVAc unit in copolymers increases with the increase of monomer conversion.The Mn of obtained PVVA was about 20000 and the PDI was about 1.6.However,the introduction of VAc has a great influence on the morphology of PVVA particles during the 2SP process.The PVVA particle size increases with the increase of the feed ratio of VAc.By using as a processing agent,PVCA can significantly promote the melting of PVC and improve the mechanical properties of PVC blends.For example,the melting time of PVC with 3 phr PVVA-5.7 was 52 s,which was 37 s faster than that of control run(PVC without additive).The tensile strength of PVC/PVVA-5.7 blend was 62.4 MPa,increased by 15.6%,the elongation at break was 54.6%,increased by 4.1 times,the impact strength of simply supported beam was 2.8 kJ/m2,increased by 2.5 times.3.A A and VCM copolymer(PVCA)with low average number molecular weight(Mn,?10000)was synthesized by 2SP.By tuning acrylic acid dropping rate,the PVCA copolymer with much more uniform copolymer composition is obtained in comparison to all monomer-in process.Subsequently,the PVCA is utilized as a novel polymer modifier for the surface treatment of CaCO3 particles and its effect on the mechanical properties of obtained rigid PVC composites are evaluated systematically.As a result,the PVCA modified CaCO3 particles exhibit uniform dispersibility and excellent compatibility in PVC matrix.The modified CaCO3 effectively promotes the melting of PVC and significantly improves the heat resistance and mechanical properties of PVC materials.When the amount of PVCA was 5 wt%,the tensile strength of PVC/CaCO3@PVCA composite was up to 46.4 MPa,which was increased by 20%compared with that of unmodified,and the elongation at break reached 119.8%,which was increased by 4 times.4.The BA-VAC-VCM terpolymer(PCBV)was prepared by precipitation polymerization.The effects of monomer feed ratio,initiator concentration,reaction temperature and solvent on the copolymer composition and particle morphology of the terpolymer were systematically investigated.When the composition of BA and VAc in PCBV is lower than 15 wt%,the glass transition temperature of PCBV is higher than the polymerization temperature,causing the precipitation of PCBV out from the solvent to form polymer particles.The polymerization mechanism is similar to the 2SP of VCM.When the composition of BA and VAc in the terpolymer increases,the glass transition temperature of the terpolymer is lower or closer to the polymerization temperature.In this case,the state of PCBV in the solvent mainly depends on the solubility of the solvent.In the poor solvent,PCBV displayed a slurry state and the polymerization mainly occurred in the solvent phase.The swelling degree of the PCBV was increased when the solubility of the solvent was enhanced.The polymerization mainly occurred in the swelling terpolymer and the gel effect was obvious.The Mn and the fraction of BA in the PCBV decreased with the increased conversion.With the increase of polymerization temperature and initiator concentration,the polymerization rate increased and the Mn of PCBV decreased.By employing PCBV as a kind of polymeric lubricant of rigid PVC,the lubrication efficiency of PCBV is much superior to those commercial ones such as SA,OPE.For example,by adding 1.5 phr PCBV-49.7 in the rigid PVC system,the melting time was prolonged by 30%and the equilibrium torque was reduced by 6.5%.The tensile strength of PVC/PCBV-49.7 reached 58.9 MPa,which was increased by 10%,and the elongation at break reached 28.5%,which was increased by 2.5 times.