The pipeline manufacturer has a turnover of more than £130m and employs 370 staff.
Professional services firm Ernst & Young in Birmingham and Manchester advised Radius' shareholders on the deal, along with Eversheds. Deloitte and CMS Cameron McKenna acted for Polyplastic Group.
"The only acquisitions we're use to hearing coming from Russia are football clubs and big London mansions – but it's something we may hear more of in the future," Insider editor Kurt Jacobs said.
"The big focus thus far has been on Russians' interest in big names and luxury brands, but increasingly we could see them showing more attention to UK industries that support its development of its huge reserves of gas, oil and precious metals. As we are keen to secure our access to fossil fuels, so they want to ensure they own the technologies that deliver them.
"The sheer raw material wealth of Russia is huge, and our economic links are growing at a huge rate. Russia's now the UK's fourth-largest export market outside Europe, China and North America – they rose 15 per cent last year to £5.5bn. The government there is spending huge amounts on economy modernisation and infrastructure development agenda, and its underpinned by 140-million consumers which match the West in appetite - if not yet spending power - for quality services and goods."
The UK business – the Hilcote head office in Alfreton and Banbridge and Lurgan in Northern Ireland – will continue to trade under the Radius Systems, Radius Plastics and Radius Plus brands.
Polyplastic Group was founded in 1991 and supplies of polyethylene piping services for infrastructure markets, with production plants in Russia, Ukraine, Belarus and Kazakhstan.
Chief executive Miron Gorilovsky said at the time: "The acquisition brings complementary technologies and innovation and reciprocal access to new markets. The strengthened group will benefit from the scale generated by the acquisition thereby creating a solid foundation for future growth."
Radius chief executive Andy Taylor added that the acquisition was "exceptionally good news" for the group and should provide "welcome reassurance" for its employees and suppliers.