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Poly-para-xylylene based polymers, also known as parylenes, are polymers that can be deposited in thin film form at room temperature by chemical vapor deposition (CVD). In the CVD process the p-xylylene monomers obtained by pyrolysis of paracyclophane polymerize into long chain molecules. The initiation of polymerization requires dimerization of two monomers leading to formation of a biradical dimer. The chain molecules grow through the propagation reaction only one unit at a time, by the attachment of a monomer to a radical chain end. In this work the polymerization of parylene is studied using all-atom molecular dynamics (MD) simulations. MD is extended with Monte Carlo step allowing for bond formation between two monomers or between an active radical chain end and a monomer. Simulations are performed for deposition of para-xylylene onto three different substrates: water, octane and silicon surface.